The present invention relates to air-filled mattresses and, in particular, it concerns a system and method employing a pneumatic mattress for the prevention and treatment of bed sores and the like.
It is known that local pressure applied to the skin disrupts the local circulatory system and can, when prolonged, lead to risk of bed sores. In healthy people, frequent body movements during even deep sleep serve to prevent prolonged application of pressure to any one site. For sick and elderly people, on the other hand, reduced mobility increases the risk of developing sores. The risks are further aggravated in people with poor circulation.
Many systems have been suggested for prevention and treatment of bed sores. One type of system employs fluid-filled cushions to distribute pressure evenly over an increased area. An example of such a system is disclosed in U.S. Pat. No. 4,949,412 to Goode. Goode discloses a closed loop feedback-controlled air supply system for air support convalescent beds. The bed is disclosed to have between 15 and 30 air cells divided along the length of the bed into five regions. Each region is maintained at a preset constant pressure value.
A similar system constructed as an overlay for a box-spring foundation is disclosed in U.S. Pat. No. 4,662,012 to Torbet. In this case, the mattress has about twenty rows of air cells divided into four zones. The cells in each zone are interconnected so as to be held at equal pressure. The overlay itself is flexible and is intended to distort as the springs give under localized pressure.
These systems have a number of major disadvantages. Firstly, they rely on a priori or manually input data in order to fix suitable pressure values. Secondly, the response of the systems is over predefined large regions, thereby precluding localized responses to specific medical conditions or body positions. Thirdly, no diagnostic information can be recovered from these systems. And finally, it is impossible to completely relieve pressure from any point of contact with the bed. The prior art overlay-type constructions suffer from the additional shortcoming that they have an inconsistent correlation between inflation pressure and body contour dependent on the properties of the underlying surface.
A second type of system uses alternate inflation and deflation of different fluid-filled support elements to cyclically relieve pressure from each point on the skin. An example of such a system is disclosed in U.S. Pat. No. 5,103,518 to Gilroy et al. Gilroy et al. disclose an alternating pressure pad as an overlay for a conventional mattress. The pad includes two sets of interspaced transverse inflatable elements which are alternately inflated and deflated. A similar system is disclosed in U.S. Pat. No. 4,852,195 to Schulman. In this case, the elements are arranged in three sets with hexagonal symmetry.
These systems also have a number of disadvantages. Firstly, the inflation pressure of all the elements is a fixed value irrespective of the part of the body being supported. Secondly, since the pressure alternates over the entire body area, discomfort may be caused to certain parts of the body which are not at risk. Thirdly, where a wound or sore already exists, the period of pressure release provided may be insufficient. And, as with the first type of system, no diagnostic information can be recovered.
There have also been attempts to produce a controllable mattress with capabilities for physical contour measurements and localized response. Examples of proposed systems of this type are disclosed in U.S. Pat. No. 4,542,547 to Sato and U.S. Pat. No. 4,799,276 to Kadish. U.S. Pat. No. 4,989,283 to Krouskop relates to a method of control for a system of this type in which the height of each cell is measured. However, these systems, if at all operable, are both over-complex and prohibitively costly to produce. Specifically, they suffer from high sensitivity to humidity and temperature leading to inaccuracy and unrepeatability of results. In addition, the use of pistons suggested by Kadish is very sensitive to transverse forces.
There is therefore a need for a pneumatic mattress providing a high resolution intelligent response to local pressure maxima, allowing complete relief of contact pressure from critical areas of the body, and generating useful diagnostic information. It would also be highly advantageous to provide a low-cost versatile pneumatic mattress system for use as part of a bed or as an overlay which is capable of providing a wide range of diagnostic, preventative and therapeutic functions.